The present invention is directed to a system for repairing tissue defects in intervertebral discs. It more particularly is concerned with repairing the portion of an intervertebral disc that has been subject to damage, such as herniation, as well as to repairing that portion of an intervertebral disc remaining after the performance of a partial discectomy intervention. Such discectomies are conventionally performed to treat a severe hernia of an intervertebral disc.
A disc hernia is a radial rupture of the annulus fibrosus of the intervertebral disc that is accompanied by a protrusion (sometimes a very large protrusion) of the annulus fibrosus and/or by an extrusion of disc material through the rupture in the annulus fibrosus. The rupture of the annulus fibrosus is often accompanied by a compression of the spinal canal and pressure on the nerve roots that pass through the disc protrusion or extrusion. This usually leads to strong and progressive pain that emanates from the compromised segment of the spine. This condition may require a surgical intervention.
Patients with a symptomatic disc hernia, and indication for a surgical intervention at the disc, normally undergo a partial or total discectomy operation. In a partial discectomy, protruding annulus disc material and a portion of the nucleus pulposus of the disc are removed. The resulting reduction in the volume of disc material within the epidural space leads to decreased pressure on the compressed nerve roots and/or the spinal cord, respectively. Without repair, the radial rupture defect in the annulus fibrosus will remain and will not close, at least it will not close in a relatively short time. Without repair, a considerable risk of post-discectomy complications, such as a re-herniation of the disc, will remain.
A successful discectomy intervention will result in lasting pain relief for the patient. However, it has been shown that severe post-discectomy complications may occur in about 6-16% of all surgical interventions. These are often caused by events such as a re-herniation of the disc, extensive epidural scar formation or vascularization and nerve ingrowth into the defect in the annulus fibrosus.
The cells of the nucleus pulposus produce cytokines and inflammatory mediators, such as nitric oxide, that have been shown to be responsible for nerve root irritation and sensitization that can lead to severe radicular pain. In a post-discectomy situation, without repair of the annulus fibrosus, nucleus pulposus material may migrate into the epidural space and/or nucleus pulposus-derived cytokines and inflammatory mediators may diffuse into the epidural space through the annulotomy site. Both events may result in post-discectomy complications such as persistent nerve root pain.
As a side effect of the volume reduction that is attendant upon a discectomy intervention, the intervertebral disc height, and thus the vertical distance between adjacent vertebral bodies, will be reduced. The decreased intervertebral disc height may be one of the reasons for a re-herniation of the disc. Further, the reduction in intervertebral disc height has been reported to lead to an accelerated mono-segmental degeneration of the annulus fibrosus or of the facet joints of the affected spinal segment.
Dr. Hansen YUAN (Professor of Medicine at Syracuse University) has recently presented a review of the available technology that is currently being exploited in connection with disc repair and replacement (13th annual meeting of the North American Spine Society, Oct. 30, 1998 in San Francisco, Calif. USA). According to an abstract of this presentation, many different people and groups are working on mechanical disc replacements, hydrogel implant replacements and in situ curable polyurethane disc replacements.
It is an important object of this invention to provide means for reducing the incidence of post-discectomy complications by closing the annulus defect that remains after a discectomy surgical intervention.
It is another object of this invention to provide an in-situ curable sealant material that provides the surgeon with means for reducing the risk of re-herniation whilst leaving as much potentially regenerating nucleus pulposus tissue as possible within the disc space.
It is another object of the invention to provide means for closure of a ruptured or incised annulus fibrosus site after discectomy sufficient to seal the compartment restraining and surrounding the nucleus pulposus (portion) of the disc and to prevent later extrusion of further disc material (recurrent disc hernia).
It is another object of the invention to prevent, by sealing the annulus fibrosus, hypertrophic scar formation, vascularization, nerve ingrowth, or infection of the ruptured annulus fibrosus or in the nucleus pulposus cavity.
It is another object of the invention to prevent, by sealing the annulus, migration of nucleus pulposus cells into the epidural space, and to prevent, by sealing the annulus, diffusion of nucleus pulposus-derived cytokines and inflammatory mediators into the epidural space through the annulotomy site. The thus resulting prevention of contact between nucleus pulposus cells, and its cytokines or inflammatory mediators, with nerve roots after discectomy is another object of the invention and will assist to minimize nucleus pulposus-induced nerve root injury and nerve root pain.
It is another object of the invention to provide means to repair a ruptured annulus fibrosus, where the means functions as a sealant for the ruptured annulus fibrosus and, provided the nucleus pulposus contains a sufficient number of viable cells, assists in the restoration of the load-bearing and viscoelastic properties of the defective intervertebral disc.
It is another objective of the invention to provide an implant that minimizes removal of nucleus pulposus material during a discectomy intervention without having an elevated risk of recurrent disc hernia. Since the nucleus pulposus tissue in most disc hernia patients is viable and has regenerative potential, leaving as much nucleus pulposus tissue as possible in the disc space may be conducive to the gradually regeneration of the disc and restoration of its physiological functions.
Other and additional objects of this invention will become apparent from a consideration of this entire specification, drawings and claims.
In accord with and fulfilling these objects, one aspect of this invention comprises the use of compositions comprising an in-situ curable sealant(s), made of a bio-compatible material, to repair defects in an annulus fibrosus of an intervertebral disc. Such defects may be fissures and ruptures of the annulus fibrosus due to disc degeneration or disc hernia, as well as injuries due to incisions and punctures of the annulus fibrosus such as from annulotomy or discectomy procedures.
In general, defects in the annulus fibrosus have the shape of a complex radial cleft that extends from the innermost edge of the annulus fibrosus, that is at the border of the nucleus pulposus, to the outermost layers of the annulus fibrosus. The defect may originate A) because of a burst canal or rupture of the annulus fibrosus that permitted extrusion there through of material from the nucleus pulposus, or, B) by reason of incisions that had to be made during surgery in order e.g. to remove nucleus pulposus material from within the intervertebral disc that has caused a large bulge or protrusion of the disc.
Another type of defect of the annulus fibrosus is often observed in the case of severely degenerated intervertebral discs. In this condition, the disc tissue has become severely dehydrated and has lost its elasticity. As a result, the annulus fibrosus tissue has become brittle, friable and unstable to the extent that tissue fragments may come loose and migrate out of the annulus fibrosus, leaving space through which nucleus pulposus material can exude. These fragments are separated from the main body of the annulus fibrosus by numerous interconnecting fissures and are often held in place only by a thin outer lamella of the annulus fibrosus (see FIG. 3 for illustration). When this thin layer tears, the fragments may migrate into the epidural space and cause pressure on the spinal nerves, that in turn may cause severe pain.